Compensated potential device circuits



June 10, 1952 J. T. CARLETON COMPENSATED POTENTIAL DEVICE CIRCUITS FiledApril 15, 1950 H.V. Line INVENTOR WITNESSES: my @0- A n o .0 e H o T s em J ATTORNEY Patented June 10, 1952 1 COMPENSATED POTENTIAL DEVICECIRCUITS James T. Carleton, Pittsburgh, Pa., asslgnor to WestinghouseElectric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania I Application April 15, 1950, Serial No. 156,106

4 Claims.

My invention relates to potential-devices such as are shown in thePeters Patent 1,819,260, granted August 18, 1931. Thesepotential-devices are adapted'to be connected to either anintermediate-voltage tap of a string of coupling capacitors, or anintermediate tap of a bushing of a circuit breaker or transformer. Ineither event, the potential-device is adapted for use with ahigh-voltage alternating-current line; the tapped capacitor or thetapped bushing reduces the linevoltage to a relatively small value, suchas 4,000 volts between the tapped point and ground, and thepotential-device includes a step-down transformer and tuning means, forreducing this tapped voltage to a still lower value, such as 115 volts.

When the voltage-coil of a high-speed impedvance-relay is operated fromsuch a potentialdevice, it has been found that faulty operations occurunder certain conditions. It has been known that these faulty operationspractically never occur within the rating of the potentialdeviee, whenthe potential-device is operating on a resistive burden, or when therest of the burden on the potential-device, other than the voltage-coilof the impedance-relay in question, draws a unitary-power-factor currentfrom the output-terminals of the potential-device. It has long beenknown that the power factor of any burden could be corrected, andbrought to unity, by the addition of suitable capacitive or inductivereactors, as the case might require, but these power-factor-correctingreactors are effective at only one frequency.

At times, an electrical system may operate, for very brief periods, atsome frequency other than the normal or rated line-frequency; and itis abroad object of my invention, therefore, to devise some sort ofcompensating-circuit, to be added to the burden or load-circuit of apotential-device or other alternating-current voltage-source, so thatthe total current drawn by the burden and the compensating device,combined, shall always have a unitary power-factor, so that the entirecombination behaves as a pure resistance, under alloperating-frequencies of the source or potential-device.

Most burdens on a potential-device are coils, which have considerableinductance, as well as resistance, so that such burdens draw laggingcurrent from the potential-device. I have found that it is possible toadd a compensating device consisting of a capacitor and a resistance,which will bring the total burden to unity power-factor at allfrequencies. It is a specific object of my invention, therefore, toprovide a compensating device having a capacitor and a resistor of theproper specific values, for accomplishing, this purpose, as willhereinafter be explained more in detail.

An exemplary form of embodiment of my invention is illustrated in theaccompanying drawing, the single figure of which is a diagram ofillustrative circuits and apparatus.

The drawing shows a conventional capacitor potential-device, connectedbetween a high-voltage line 5 and the ground 6, and comprising acapacitance-divider 1 which may be either a coupling capacitor or acondenser-bushing, represented by three capacitors C1, C2 and C3.capacitance-divider 1 is shown as having a tapped point 8, which usuallyprovides about 4,000 volts above ground. r

The tap 8 of the capacitance-divider l is used to energize the primaryinput-circuit of a stepdown potential-transformer T. The step-downtransformer T has a secondary output-circuit 9 which is connected to theburden B. The secondary output circuit 9 necessarily contains some sortof means for adjusting the equivalent leakage-reactance of the step-downtransformer T, so as, in effect, to make this equivalentleakagereactance substantially equal tothe equivalent capacitivereactance of the source or divider. In the drawing, thisleakage-reactance adjusting-means is shown as a variable or tunableinductance Lt, but it is to be understood that, this representation isintended to indicate either a variable reactor, separatefrom thetransformer T and serially connected within the secondary output-circuit9 thereof, or the variable-reactance part of the leakage-reactance of avariable-leakage-reactance transformer T. In this way, the equivalentcapacitive reactance X of the source is tuned out, so that theregulation of the secondary output-circuit 9 will be smalhand thevoltage of this circuit will be in phase with the voltage of thehigh-voltage line 5 during steady operating-conditions.

In the drawing, the voltage of the output-circuit 9 of thepotential-device is indicated as E, and the burden B is represented asincluding a serially connected inductance L and resistance R, drawing acurrent I. Usually, the burden B on a potential-device will consist'of anumber of voltage-coils or load-circuits in parallel with each other,and the indicated burden, in the drawing, is intended to represent theequivalent of! the total burden, with a sufliciently closeapproximation. Thus, if the total budren-current is a cur- The renthaving a magnitude i, at a power-factor cos 0, the total volt-ampereburden would obviously be (ET), the equivalent resistance would be 213:2 cos (l) 1 (E1) and the total inductive reactance would be E E EX=2. L= 6:: 1- os 6= l-cos 6 'rf 1 sin 1 c EI\/ (2) whence theequivalent inductance L, in henrys, would be In accordance with myinvention, I apply a compensator-burden B, in parallel to the burden B,across the output-terminals 9 of the potentialdevice. This compensatingburden B consists of a capacitor C and a resistor R connected in serieswith each other. In order to achieve the objects of my invention, theresistance R must be the same in both the real burden B and thecompensator-burden B, and the value of the capacitance C of thecompensator-capacitor, in farads, should be related to the inductance Land the resistance R of the burden B by the relation,

The effect of the above-described combination of a burden B and acompensating burden B is to provide a combined impedance Z which acts asa pure resistance at all frequencies. Thus, the combined impedance Z ofthe two parallel-connected burdens B and B' is Equation 6 thus showsthat the combined effect of my compensating burden B and the regularburden B will be the same as if the total of the two burdens were simplythe resistance R, regardless of the frequency f or the angular velocity10:21

The value of the compensating capacitor C can be expressed in terms ofthe volt-ampere burden (ET), the voltage E, the power-factor cos 0, andthe frequency f at which said power-factor is measured, by combiningEquations 1, 3 and 4. Thus,

With such a compensation, the potential device has a pure-resistanceload, under all frequencyconditions, and hence no faultyrelay-operations are obtained if the potential-coil HZ of a highspeedimpedance-relay, or other critical device, is connnected, as anadditional load, across the same potential-device, as shown in thedrawing.

Since the burden of the impedance-relay voltagecoil HZ is usually quitesmall, as compared to the total burden on the potential-device, thiscoil HZ may be added after the rest of the burden has been compensated,as above described, or the burden of the voltage-coil HZ could beincluded in the equivalent-circuit burden B which is represented by asingle equivalent inductance L and a single equivalent inductance R,representing all of the burdens combined, except for the compensatingburden B which is added in accordance with my invention.

Equation 4 states that the compensatorcapacitance C, in farads, is equalto L/R where L is the inductance, in nenrys, and R is the resistance, inohms, of the equivalent combined impedance of all of theparallel-connected burdens which are being compensated. It is notnecessary for each of these parallel-connected burdens to have preciselythe same ratio of inductance to resistance. The necessary value 01 thecompensating reactance C depends only on the impedance of the totalburden, as stated. Sometimes, acceptable results are obtained when thevalue of the compensating impedance (R7/wC) only approximately satisfiesthe re-, quired conditions, which are: (a) that thecompensator-resistance shall be equal to the total or equivalentburden-resistance, and (b) that the compensator-capacitance shall beequal to the equivalent burden-inductance divided by the square of theequivalent burden-resistance.

While I have described my invention in accordance with a singleillustrative form or embodiment, and in connection with a particularrelaying-problem involving high-speed impedancerelays, I wish it to beunderstood that my invention is not altogether limited in theseparticulars. I desire, therefore, that the appended claims shall beaccorded the broadest construction con sistent with their language.

I claim as my invention:

1. The combination of an alternating-current input-circuit, a burdenconnected thereto and having any equivalent burden-inductance and anyequivalent serially connected burden-resistance, and acapacitive-impedance compensatordevice connected in shunt to said burdenand having a compensator-resistance which is substantially equal to theequivalent burden-resist-. ance, and a serially connectedcompensatorcapacitance (in farads) which is substantially equal to theequivalent burden-inductance (in henrys) divided by the square of theequivalent burden-resistance (in ohms), whereby the combined load onsaid input-circuit is substantially a pure resistance over a range offrequencies of the input circuit.

2. The combination with an alternating-current power-line, of apotential-device including a tapped capacitance-divider for supplying 9,reduced line-voltage, a burden connected thereto and having anyequivalent serially connected burden-inductance and any equivalentburdenresistance, and a capacitive impedance compensator-deviceconnected in shunt to said burden and having a compensator-resistancewhich is substantially equal to the equivalent burdenresistance, and aserially connected compensatorcapacitance (in farads) which issubstantially equal to the equivalent burden-inductance (in henrys)divided by the square of the equivalent burden-resistance (in ohms),whereby the combined load on said capacitance-divider is subing areduced line-voltage, a burden connected thereto, including thevoltage-coil of a high-speed impedance-relay connected in shunt acrossthe output-circuit of said potential-device, said burden having anyequivalent burden-inductance and any equivalent serially connectedburdenresistance, and a capacitive-impedance compensator-deviceconnected in shunt to said burden and having a compensator-resistancewhich is substantially equal to the equivalent burdenresistanoe, and aserially connected compensatorcapacitance (in farads) which issubstantially equal to the equivalent burden-inductance (in henrys)divided by the square of the equivalent burden-resistance (in ohms),whereby the combined load on said potential-device is substantially apure resistance over a range of frequencies of the power-line.

4. The combination with an alternating-current power-line, of apotential-device including a tapped capacitance-divider for deriving areduced line voltage, a burden connected thereto, including thevoltage-coil of a high-speed impedancerelay connected in shunt acrossthe output circuit of said potential-device, said burden having anyequivalent burden-inductance and any equivalent serially connectedburden-resistance.

and a capacitive-impedance compensator-device connected in shunt to saidburden and having a compensator-resistance which is substantially equalto the equivalent burden-resistance, and a serially connectedcompensator-capacitance (in farads) which is substantially equal to theequivalent burden-inductance (in henrys) divided by the square of theequivalent burden-resistance (in ohms), whereby the combined load onsaid potential-device is substantially a pure resistance over a range offrequencies of the powerline, and whereby said impedance-relay issubstantially free of faulty operations within the rating of thepotential device, notwithstanding deviations in the line-frequency.

JAMES T. CARLETON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,376,399 Chubb May 3, 19211,795,207 Frick Mar. 3, 1931 1,819,260 Peters Aug. 18, 1931 1,924,307Creighton Aug. 29, 1933 1,950,676 Higgins Mar. 13, 1934 2,186,486Higgins Jan. 9, 1940 2,503,739 Hanssen Apr. 11, 1950

